This invention relates to liquid chromatographic columns and more particularly to fittings for holding the frit in place at the outlet of the column.
It is known to hold the packing in place in a liquid chromatographic column with a porous frit, which has sufficient stiffness and strength to hold the packing against substantial thrust pressure during operation of the chromatograph. The frit is held in place by a threaded fitting.
In a first prior art fitting of the known class, the frit is held by a threaded sleeve having a tapered swage or conical surface against which the column is sealed by threaded pressure on a conical ferrule. The frit has a diameter substantially equal to the outer diameter of the column.
In a second prior art fitting of the known class, the frit is held in a plastic ring, such as Kel-F ring, so the frit matches the inner diameter of the column.
The first prior art fitting has several disadvantages, such as: (1) the liquid extends through the frit beyond the inside diameter of the column and this causes some tailing; and (2) the seal is at the tapered joint and thus liquid may flow to that point, causing further tailing. The second type of fitting also has a disadvantage in that, if the plastic ring is compressed with use, or if the plastic ring or frit are too large or too small causing the seal around the column to open, liquid fills the cracks and voids to create tailing.